The present invention concerns devices computer systems and pertains particularly to detection when a detachable device has been disconnected from a host device.
Detachable devices, such as plug-in cards, are used to provide additional functionality to computer systems or other host devices. For example, plug-in cards can provide additional memory, additional communication capability and/or additional processing capability to a portable computer or a personal digital assistant (PDA).
For proper performance, it is often desirable for a plug-in card to detect when the plug-in card has been disconnected from the host system. This is done, for example, by monitoring a first end of a resistor. A second end of the resistor is connected to the voltage (VBattery) supplied by the battery internal to the plug-in card. When the plug-in card is connected to a card slot within a computer or other device, the first end of the resistor is connected to a ground by the card slot within the computer and thus the voltage level of the first end of the resistor is at 0 volts. When the plug-in card is disconnected to the computer, the first end is open. In this case the voltage on the first end of the resistor floats to VBattery.
While this is an effective way to detect whether a plug-in card is connected or disconnected to a host device, the drain of current through the resistor can shorten the battery life of the battery within the plug-in card.